Help a non-plumber: Vent failure

Hi, I live on the first floor of a three story house/apartment building. Recently, I’ve had the problem that the water traps in my bathroom and kitchen are being siphoned about once a day. I realize it’s probably due to faulty design of the vents when the building was converted to apartments, and is occurring when somebody upstairs empties their tub or something. My question is, would the ventilation problem be at their traps (near the roof) or at mine? Also, how often is this type of problem caused by clogs or something in the vent? I didn’t notice it for the first year I lived here, so I want to say it’s only been happening recently.

Bill